1. Field of Invention
The invention relates to circuit of inductance/capacitance (LC) voltage-controlled oscillator.
2. Description of Related Art
It needs to consider several factors for the performance of inductance/capacitance (LC) voltage-control oscillator (LC VCO) in the current wireless communication system, including phase noise and tuning rage of frequency. In order to have both these characteristics, a mechanism of switching capacitance is usually taken. It can reduce the gain (Kvco) of the LC VCO, so as to obtain a relative level of phase noise while the tuning rage of frequency can still be wide.
However, the inductance quality factor (Q) of the LC VCO operated at different frequencies may vary in a large range. This causes a difficulty to obtain a proper phase noise for all operation frequency of the LC VCO. In addition, the output amplitude is also varying in a large range. This also causes the difficulty to design the buffer and frequency mixer, which are coupled after the LC VCO. Further, it may also cause a lot of power consumption.